Compound semiconductors and their application

ABSTRACT

Disclosed are new compound semiconductors which may be used for solar cells or as thermoelectric materials, and their application. The compound semiconductor may be represented by a chemical formula: In x M y Co 4-m-a A m Sb 12-n-z X n Te z , where M is at least one selected from the group consisting of Ca, Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Ag, Cd, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; A is at least one selected from the group consisting of Fe, Ni, Ru, Rh, Pd, Ir and Pt; X is at least one selected from the group consisting of Si, Ga, Ge and Sn; 0&lt;x&lt;1; 0&lt;y&lt;1; O≦m≦1; 0≦n&lt;9; 0&lt;z≦2 and 0&lt;a≦1.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/KR2012/003729 filed on May 11, 2012, which claims priority to KoreanPatent Application No. 10-2011-0045348 filed on May 13, 2011, KoreanPatent Application No. 10-2011-0045349 filed on May 13, 2011, KoreanPatent Application No. 10-2011-0049609 filed on May 25, 2011 and KoreanPatent Application No. 10-2012-0050257 filed on May 11, 2012 in theRepublic of Korea, the entire contents of which are incorporated hereinby reference.

TECHNICAL FIELD

The present disclosure relates to a new compound semiconductor materialwhich may be used for solar cells or as thermoelectric materials, itspreparation method, and its applications.

BACKGROUND ART

A compound semiconductor is not a single element such as silicon andgermanium but a compound having two or more kinds of combined elementsserving as a semiconductor. Various kinds of compound semiconductorshave been developed and used in many fields. For example, a compoundsemiconductor may be used for thermoelectric conversion devices using aPeltier effect, light emitting devices such as light emitting diodes andlaser diodes using a photoelectric conversion effect, solar cells, orthe like.

Among these, the thermoelectric conversion device may be applied tothermoelectric conversion generation, thermoelectric conversion coolingor the like. Here, in the thermoelectric conversion generation, athermal electromotive force generated by applying a temperaturedifference to the thermoelectric conversion device is used forconverting thermal energy to electric energy.

The energy conversion efficiency of the thermoelectric conversion devicedepends on ZT which is a performance index of the thermoelectricconversion material. Here, ZT is determined according to a Seebeckcoefficient, electric conductivity, thermal conductivity, or the like.In more detail, ZT is proportional to the square of the Seebeckcoefficient and the electric conductivity and is inversely proportionalto the thermal conductivity. Therefore, in order to enhance the energyconversion efficiency of the thermoelectric conversion device,development of a thermoelectric conversion material with a high Seebeckcoefficient, a high electric conductivity, or a low thermal conductivityis desired.

Meanwhile, a solar cell is environment-friendly since it does not needan energy source other than solar rays, and therefore are activelystudied as an alternative future energy source. A solar cell may begenerally classified as a silicon solar cell using a single element ofsilicon, a compound semiconductor solar cell using a compoundsemiconductor, and a tandem solar cell where at least two solar cellshaving different band gap energies are stacked.

Among these, a compound semiconductor solar cell uses a compoundsemiconductor in a light absorption layer which absorbs solar rays andgenerates an electron-hole pair, and may particularly use compoundsemiconductors in the III-V group such as GaAs, InP, GaAlAs and GaInAs,compound semiconductors in the II-VI group such as CdS, CdTe and ZnS,and compound semiconductors in the group represented by CuInSe₂.

The light absorption layer of the solar cell demands excellent long-termelectric and optical stability, high photoelectric conversionefficiency, and easy control of the band gap energy or conductivity bycomposition change or doping. In addition, conditions such as productioncost and yield should also be met for practical use. However, manyconventional compound semiconductors fail to meet all of theseconditions at once.

DISCLOSURE Technical Problem

The present disclosure is designed to solve the problems of the priorart, and therefore it is an object of the present disclosure to providea new compound semiconductor material, which may be utilized in variousways for thermoelectric conversion materials of thermoelectricconversion devices, solar cells or the like, a preparation methodthereof, and a thermoelectric conversion device or solar cell using thesame.

Other objects and advantages of the present disclosure will beunderstood from the following descriptions and become apparent by theembodiments of the present disclosure. In addition, it is understoodthat the objects and advantages of the present disclosure may beimplemented by components defined in the appended claims or theircombinations.

Technical Solution

In one aspect, after repeated studies of a compound semiconductor,inventors of the present disclosure have successfully synthesized acompound semiconductor represented by Chemical Formula 1, and found thatthis compound can be used for a thermoelectric conversion material of athermoelectric conversion device or a light absorption layer of a solarcell.

Chemical Formula 1

In_(x)M_(y)Co_(4-m-a)A_(m)Sb_(12-n-z)X_(n)Te_(z)

In the Chemical Formula 1, M is at least one selected from the groupconsisting of Ca, Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Ag, Cd, Sc, Y, La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; A is at least oneselected from the group consisting of Fe, Ni, Ru, Rh, Pd, Ir and Pt; Xis at least one selected from the group consisting of Si, Ga, Ge and Sn;0<x<1; 0<y<1; 0≦m≦1; 0≦n<9; 0<z≦2 and 0<a≦1.

Preferably, in Chemical Formula 1, 0<x≦0.25.

Also preferably, in Chemical Formula 1, 0≦m≦0.5.

Also preferably, in Chemical Formula 1, 0<a≦0.5.

Also preferably, in Chemical Formula 1, 0<x+y≦1.

Also preferably, in Chemical Formula 1, 0<n+z<9.

In another aspect, the present disclosure also provides a preparationmethod of a compound semiconductor, which includes: mixing In, Co, Sband Te as well as at least one selected from the group consisting of Ca,Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Ag, Cd, Sc, Y, La, Ce, Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and their oxides; and thermally treatingthe mixture formed in the mixing step.

Preferably, the mixture formed in the mixing step further contains atleast one selected from the group consisting of Fe, Ni, Ru, Rh, Pd, Ir,Pt and their oxides.

Also preferably, the mixture formed in the mixing step further containsat least one selected from the group consisting of Si, Ga, Ge, Sn andtheir oxides.

Also preferably, the thermally treating step is performed at 400° C. to800° C.

Also preferably, the thermally treating step includes at least twothermal treatment stages.

In another aspect, the present disclosure also provides a thermoelectricconversion device, which includes the compound semiconductor as above.

In another aspect, the present disclosure also provides a solar cell,which includes the compound semiconductor as above.

Advantageous Effects

According to the present disclosure, a new compound semiconductormaterial is provided.

In one aspect, the new compound semiconductor may replace a conventionalcompound semiconductor or may be used as another material in addition tothe conventional compound semiconductor.

Further, in one aspect of the present disclosure, since the compoundsemiconductor has good thermoelectric conversion performance, it may beused for a thermoelectric conversion device. In particular, the compoundsemiconductor according to the present disclosure may have an improvedZT value, which is a thermoelectric performance index, since the thermalconductivity is improved. Therefore, the compound semiconductoraccording to the present disclosure may be used as a thermoelectricconversion material of a thermoelectric conversion device.

In addition, in another aspect of the present disclosure, the compoundsemiconductor may be used for a solar cell. Particularly, the compoundsemiconductor of the present disclosure may be used as a lightabsorption layer of the solar cell.

Moreover, in another aspect of the present disclosure, the compoundsemiconductor may be used for an IR window or IR sensor whichselectively passes IR, a magnetic device, a memory or the like.

DESCRIPTION OF DRAWINGS

Other objects and aspects of the present disclosure will become apparentfrom the following descriptions of the embodiments with reference to theaccompanying drawing in which:

FIG. 1 is a graph showing thermal conductivity values according to atemperature change of compound semiconductors according to an exampleaccording to the present disclosure and a comparative example.

PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure based on the principle that the inventor is allowed to defineterms.

Therefore, the description proposed herein is just a preferable examplefor the purpose of illustration only, and is not intended to limit thescope of the disclosure, so it should be understood that otherequivalents and modifications could be made thereto without departingfrom the spirit and scope of the disclosure.

The present disclosure provides a new compound semiconductor representedby Chemical Formula 1 below.

Chemical Formula 1

In_(x)M_(y)Co_(4-m-a)A_(m)Sb_(12-n-z)X_(n)Te_(z)

In the Chemical Formula 1, M is at least one selected from the groupconsisting of Ca, Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Ag, Cd, Sc, Y, La, Ce,Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; A is at least oneselected from the group consisting of Fe, Ni, Ru, Rh, Pd, Ir and Pt; andX is at least one selected from the group consisting of Si, Ga, Ge andSn.

In addition, in the Chemical Formula 1, 0<x<1, 0<y<1, 0≦m≦1, 0≦n<9,0<z≦2, and 0<a≦1.

Preferably, in Chemical Formula 1, 0<x≦0.25.

Also preferably, in Chemical Formula 1, 0≦m≦0.5.

Also preferably, in Chemical Formula 1, 0<a≦0.5.

Also preferably, in Chemical Formula 1, 0<x+y≦1.

Also preferably, in Chemical Formula 1, 0<n+z<9.

More preferably, in Chemical Formula 1, 0<n+z<5.

Most preferably, in Chemical Formula 1, 0<n+z<3.

Meanwhile, the compound semiconductor represented by Chemical Formula 1may include a secondary phase partially, and the amount of the secondaryphase may vary depending on a thermal treatment condition.

The above compound semiconductor may be prepared by forming a mixturecontaining In, Co, Sb and Te as well as at least one selected from thegroup consisting of Ca, Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Ag, Cd, Sc, Y,La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and their oxides;and thermally treating the mixture.

Preferably, in the mixture forming step, the mixture may further containat least one selected from the group consisting of Fe, Ni, Ru, Rh, Pd,Ir, Pt and their oxides.

Also preferably, in the mixture forming step, the mixture may furthercontain at least one selected from the group consisting of Si, Ga, Ge,Sn and their oxides.

Meanwhile, each material used in the mixture forming step may be in apowder form, but the present disclosure is not limited to a specificform of the material.

Also preferably, the thermally treating step may be performed in vacuumor in a gas such as Ar, He and N₂, partially containing hydrogen or notcontaining hydrogen.

At this time, the thermally treating temperature may be 400° C. to 800°C. Preferably, the thermally treating temperature may be 450° C. to 700°C. More preferably, the thermally treating temperature may be 500° C. to650° C.

Meanwhile, the thermally treating step may include at least two thermaltreatment stages. For example, a first thermal treatment may beperformed at a first temperature to the mixture obtained in the mixtureforming step, namely in the step of mixing materials, and a secondthermal treatment may be performed thereto at a second temperature.

Here, some of the thermal treatment stages may be performed during themixture forming step where materials are mixed is executed.

For example, the thermally treating step may include three thermaltreatment stages composed of a first thermal treatment stage, a secondthermal treatment stage and a third thermal treatment (sintering) stage.In addition, the first thermal treatment stage may be performed in atemperature range of 400° C. to 600° C., and the second and thirdthermal treatment stages may be performed in a temperature range of 600°C. to 800° C. The first thermal treatment stage may be performed duringthe mixture forming step, and the second and third thermal treatmentstages may be performed in order after the mixture forming step.

A thermoelectric conversion device according to the present disclosuremay include the compound semiconductor described above. In other words,the compound semiconductor according to the present disclosure may beused as a thermoelectric conversion material for the thermoelectricconversion device. Particularly, the compound semiconductor according tothe present disclosure has a large ZT value, which is a performanceindex of the thermoelectric conversion material. In addition, due to lowthermal conductivity, a high Seebeck coefficient and high electricconductivity, the compound semiconductor has excellent thermoelectricconversion performance. Therefore, the compound semiconductor accordingto the present disclosure may replace a conventional thermoelectricconversion material or may be used for a thermoelectric conversiondevice in addition to the conventional compound semiconductor.

In addition, a solar cell according to the present disclosure mayinclude the compound semiconductor above. In other words, the compoundsemiconductor according to the present disclosure may be used for asolar cell, particularly as a light absorption layer of the solar cell.

The solar cell may be produced in a structure where a front surfacetransparent electrode, a buffer layer, a light absorption layer, a rearsurface electrode and a substrate are laminated in order from the sidewhere a solar ray is incident. The substrate located at the lowestportion may be made of glass, and the rear surface electrode on theentire surface thereof may be formed by depositing metal such as Mo.

Subsequently, the compound semiconductor according to the presentdisclosure may be laminated on the rear surface electrode by means of anelectron beam deposition method, a sol-gel method, or a PLD (PulsedLaser Deposition) to form the light absorption layer. On the lightabsorption layer, a buffer layer for buffering the difference in latticeconstants and band gaps between a ZnO layer serving as the front surfacetransparent electrode and the light absorption layer may be present. Thebuffer layer may be formed by depositing a material such as CdS by meansof CBD (Chemical Bath Deposition) or the like. Next, the front surfacetransparent electrode may be formed on the buffer layer by means ofsputtering or the like as a ZnO film or a ZnO and ITO laminate.

The solar cell according to the present disclosure may be modified invarious ways. For example, it is possible to manufacture a tandem solarcell where a solar cell using the compound semiconductor according tothe present disclosure as the light absorption layer is laminated. Inaddition, the solar cell laminated as described above may employ a solarcell using silicon or another known compound semiconductor.

In addition, it is possible to change a band gap of the compoundsemiconductor according to the present disclosure and laminate aplurality of solar cells which use compound semiconductors havingdifferent band gaps as the light absorption layer. The band gap of thecompound semiconductor according to the present disclosure may beadjusted by changing a composition ratio of a component of the compound,particularly Te.

In addition, the compound semiconductor according to the presentdisclosure may also be applied to IR windows or IR sensors whichselectively pass IR.

EXAMPLES

Hereinafter, embodiments of the present disclosure will be described indetail. The embodiments of the present disclosure, however, may takeseveral other forms, and the scope of the present disclosure should notbe construed as being limited to the following examples. The embodimentsof the present disclosure are provided to more fully explain the presentdisclosure to those having ordinary knowledge in the art to which thepresent disclosure pertains.

Example

0.0494 g of In, 0.0112 g of Zn, 0.3648 g of Co, 0.0531 g of Rh, 2.2612 gof Sb, 0.0408 g of Sn, and 0.2194 g of Te were prepared as reagents, andwere mixed by using mortar. The materials mixed as above were put into asilica tube and vacuum-sealed and then heated at 650° C. for 36 hours.The time for raising the temperature to 650° C. was 1 hour and 30minutes, and In_(0.25)Zn_(0.1)Co_(3.6)Rh_(0.3)Sb_(10.8)Sn_(0.2)Te powderwas obtained.

A part of the composed materials prepared above was formed into a diskhaving a diameter of 10 mm and a thickness of 1 mm. After that, apressure of 200 MPa was applied thereto by using a CIP (Cold IsostaticPressing). Subsequently, the obtained result was put into a quartz tubeand vacuum-sintered for 12 hours.

In regard to the sintered disk, thermal conductivity (κ) was measured byusing LFA457 (Netzsch, Inc) at predetermined temperature intervals. Themeasurement result is shown in FIG. 1 as Example.

Comparative Example

In, Co and Sb were prepared as reagents, and were mixed by using mortarto make a mixture having compositions of In_(0.25)Co₄Sb₁₂ in a pelletform. The mixture was heated at 500° C. for 15 hours under H₂ (1.94%)and N₂ gas. The time for raising the temperature to 500° C. was 1 hourand 30 minutes.

The materials mixed as above were put in a silica tube andvacuum-sealed, and then were heated at 650° C. for 36 hours. The timefor raising the temperature to 650° C. was 1 hour and 30 minutes, andIn_(0.25)Co₄Sb₁₂ powder was obtained.

A part of the material prepared above was formed into a disk having adiameter of 10 mm and a thickness of 1 mm. After that, a pressure of 200MPa was applied thereto by using a CIP. Subsequently, the obtainedresult was put into a quartz tube and vacuum-sintered for 12 hours.

In regard to the sintered disk, thermal conductivity (κ) was measured byusing LFA457 (Netzsch, Inc). The measurement result is shown in FIG. 1as Comparative Example.

Referring to the results shown in FIG. 1, it could be found that thecompound semiconductor according to the Example of the presentdisclosure expressed byIn_(0.25)Zn_(0.1)Co_(3.6)Rh_(0.3)Sb_(10.8)Sn_(0.2)Te has very lowthermal conductivity (κ) over the entire temperature measurement regionin comparison to the compound semiconductor according to the ComparativeExample expressed by In_(0.25)Co₄Sb₁₂.

In addition, the ZT value which is a thermoelectric performance indexcan be expressed as follows:

ZT=σS ² T/κ

Here, σ represents electric conductivity, S represents a Seebeckcoefficient, T represents temperature, and κ represents thermalconductivity

The compound semiconductor according to the present disclosure may havean improved ZT value since the thermal conductivity is low. Therefore,the compound semiconductor according to the present disclosure may beregarded as having excellent thermoelectric conversion and so can bevery useful as a thermoelectric conversion material.

The present disclosure has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the disclosure, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the disclosure will become apparent to those skilledin the art from this detailed description.

1. A compound semiconductor, represented by Chemical Formula 1 below:Chemical Formula 1In_(x)M_(y)Co_(4-m-a)A_(m)Sb_(12-n-z)X_(n)Te_(z) where, in the ChemicalFormula 1, M is at least one selected from the group consisting of Ca,Sr, Ba, Ti, V, Cr, Mn, Cu, Zn, Ag, Cd, Sc, Y, La, Ce, Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu; A is at least one selected from thegroup consisting of Fe, Ni, Ru, Rh, Pd, Ir and Pt; X is at least oneselected from the group consisting of Si, Ga, Ge and Sn; 0<x<1; 0<y<1;0≦m≦1; 0≦n<9; 0<z≦2 and 0<a≦1.
 2. The compound semiconductor accordingto claim 1, wherein, in Chemical Formula 1, 0<x≦0.25.
 3. The compoundsemiconductor according to claim 1, wherein, in Chemical Formula 1,0≦m≦0.5.
 4. The compound semiconductor according to claim 1, wherein, inChemical Formula 1, 0<a≦0.5.
 5. The compound semiconductor according toclaim 1, wherein, in Chemical Formula 1, 0<x+y≦1.
 6. The compoundsemiconductor according to claim 1, wherein, in Chemical Formula 1,0<n+z<9.
 7. A preparation method of a compound semiconductor,comprising: forming a mixture containing In, Co, Sb and Te as well as atleast one selected from the group consisting of Ca, Sr, Ba, Ti, V, Cr,Mn, Cu, Zn, Ag, Cd, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, Lu and their oxides; and thermally treating the mixture, therebypreparing the compound semiconductor defined in claim
 1. 8. Thepreparation method of a compound semiconductor according to claim 7,wherein the mixture further contains at least one selected from thegroup consisting of Fe, Ni, Ru, Rh, Pd, Ir, Pt and their oxides.
 9. Thepreparation method of a compound semiconductor according to claim 7,wherein the mixture further contains at least one selected from thegroup consisting of Si, Ga, Ge, Sn and their oxides.
 10. The preparationmethod of a compound semiconductor according to claim 7, wherein thethermally treating step is performed at 400° C. to 800° C.
 11. Thepreparation method of a compound semiconductor according to claim 7,wherein the thermally treating step includes at least two thermaltreatment stages.
 12. A thermoelectric conversion device, which includesthe compound semiconductor defined in claim
 1. 13. A solar cell, whichincludes the compound semiconductor defined in claim 1.